Overtravel pressure relief for a gas spring

ABSTRACT

A piston rod housing assembly for a gas spring includes a piston rod housing having an interior end, an exterior end axially spaced from the interior end, and an overtravel pressure relief passage extending through the piston rod housing and intersecting the exterior end.

This is a continuation-in-part of U.S. patent application Ser. No.14/031,900, filed Sep. 19, 2013, and of its U.S. Provisional PatentApplication No. 61/799,719, filed Mar. 15, 2013, the benefit of both ofwhich are claimed herein and the disclosure of both of which isincorporated herein by reference in their entirety.

TECHNICAL FIELD

This invention relates generally to gas springs and, more particularly,to overtravel pressure relief features for gas springs.

BACKGROUND

Gas springs are well known and have been used in dies of presses forsheet metal stamping operations. For example, gas springs can be used aspress cushions, among many other types of applications. A conventionalgas spring includes a casing, a piston rod carried in the casing, abearing and seal housing held in the casing by a retainer to guide andretain the piston rod within the casing, and a pressure chamber to holdpressurized gas, typically nitrogen at an operating pressure of, forexample, 2,000 to 5,000 PSI in some applications. The housing includesone or more bearings to guide movement of the piston rod within thecasing, and one or more seals to prevent leakage from the pressurechamber. The pressurized gas biases the piston rod to an extendedposition, and yieldably resists movement of the piston rod from theextended position to a retracted position. But the piston rod mayovertravel beyond a design-intent retracted position, and suchovertravel may result in undesirable overpressure and other conditions.

SUMMARY

In at least one implementation, a piston rod housing assembly for a gasspring includes a piston rod housing including an interior end, anexterior end axially spaced from the interior end, and an overtravelpressure relief passage extending through the piston rod housing andintersecting the exterior end.

Some potential objects, features and advantages of the gas spring and/orits components set forth herein include providing a device that isreadily usable with a wide range of forming equipment, readily permitsuse of common components among gas springs of different configurationand construction, can be easily serviced and its components replaced asneeded, can be used in a wide range of applications having differentsize and force requirements, is readily adaptable to a wide range ofpress configurations, includes an overtravel pressure relief feature,and is of relatively simple design, economical manufacture and assembly,robust, durable, reliable and in service has a long useful life. Ofcourse, an apparatus embodying the present invention may achieve none,some, all or different objects, features or advantages than those setforth with regard to the illustrative embodiments disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of preferred embodiments and bestmode will be set forth with regard to the accompanying drawings inwhich:

FIG. 1 is a top view of a presently preferred form of a gas spring withan overtravel pressure relief member;

FIG. 2 is an enlarged sectional view of the gas spring of FIG. 1, takenalong line 2-2 of FIG. 1, illustrating a piston in an overtravelposition with respect to a casing;

FIG. 3 is an enlarged fragmentary sectional view of a portion of the gasspring of FIG. 1, taken from oval 3 of FIG. 2;

FIG. 4 is a fragmentary sectional view of a presently preferred form ofan assembly of a piston rod housing and an overtravel pressure reliefmember;

FIG. 5 is an enlarged fragmentary sectional view of the housing andmember of FIG. 4, wherein the member is illustrated as ruptured from anovertravel condition;

FIG. 6 is a fragmentary sectional view of another presently preferredform of an assembly of a piston rod housing and an overtravel pressurerelief member;

FIG. 6A is a side view of another presently preferred form of anovertravel pressure relief member;

FIG. 6B is an end view of the member of FIG. 6A;

FIG. 7 is an enlarged fragmentary sectional view of the housing andmember of FIG. 6, wherein the housing is illustrated as ruptured from anovertravel condition;

FIG. 8 is a fragmentary sectional view of another presently preferredform of an assembly of a piston rod housing and an overtravel pressurerelief member employing a pin that is directly actuated by a platedriver;

FIG. 9 is a an enlarged fragmentary sectional view of the end of the pinthat is employed in the embodiment of FIG. 8;

FIG. 10 is a fragmentary sectional view of another presently preferredform of an assembly of a piston rod housing and an overtravel pressurerelief member employing a housing fitting that is directly actuated by aplate driver;

FIG. 11 is an enlarged fragmentary sectional view of the embodiment ofFIG. 10;

FIG. 12 is a side view of a housing fitting of FIGS. 10 and 11,illustrating the fitting in a ruptured condition;

FIG. 13 is a perspective view of the fitting of FIGS. 10 and 11,illustrating the fitting in an unruptured condition;

FIG. 14 is a fragmentary sectional view of another presently preferredform of an assembly of a piston rod housing and an overtravel pressurerelief member with a housing fitting that is directly actuated by a die;

FIG. 15 is an enlarged fragmentary sectional view of a pin of theembodiment of FIG. 14;

FIG. 16 is a perspective view of the pin of the embodiment of FIG. 14;

FIG. 17 is a fragmentary sectional view of another presently preferredform of an assembly of a piston rod housing and an overtravel pressurerelief member with a pin that is directly actuated by a die;

FIG. 18 is a top view of an additional presently preferred form of anassembly of a piston rod housing and an overtravel pressure reliefmember;

FIG. 19 is a side view of the assembly of FIG. 18;

FIG. 20 is a cross-sectional view of the assembly of FIG. 18;

FIG. 21 is an enlarged, fragmentary view of a portion of the assembly asillustrated in FIG. 20;

FIG. 22 is a front view of the relief member of FIG. 18;

FIG. 23 is a side view of the relief member of FIG. 18;

FIG. 24 is a cross-sectional view of a further presently preferred formof an assembly of a piston rod housing and an overtravel pressure reliefmember;

FIG. 25 is an enlarged, fragmentary view of a portion of the assembly asillustrated in FIG. 24;

FIG. 26 is a fragmentary sectional view of a presently preferred form ofa piston rod housing having an integral overtravel pressure reliefmember; and

FIG. 27 is a fragmentary sectional view of the piston rod housing ofFIG. 26.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring in more detail to the drawings, FIG. 1 illustrates a gasspring 10 that may be used in forming equipment, for example, sheetmetal stamping dies and mechanical presses (not shown). In general, thegas spring 10 may include a casing 12, a guide and seal assembly 14carried by the casing 12, a piston rod 16 carried by the casing 12 andextending through the guide and seal assembly 14, and a pressure chamber17. An outer axial end of the piston rod 16 may be engageable with or bya die member or another portion of a press or piece of forming equipment(not shown).

For example, one or more of the gas springs 10 may be used in variousimplementations in forming equipment to provide a moveable component forsupport of a forming die or a workpiece with a yielding force or areturn force. For example, in a binder ring implementation, the gasspring 10 may provide a yielding force against a binder ring of aforming die to hold a metal workpiece while another part of the formingdie forms, cuts, stretches, or bends the workpiece. In a lifterimplementation, the gas spring 10 may provide a yielding force andreturn force to lift a workpiece off of a surface of the forming die orto otherwise maintain control of the workpiece. In a cam toolimplementation, the gas spring 10 may apply a yielding force to return acam-activated tool to its home position. Of course, the gas spring 10may be used in a wide range of other implementations.

According to the present disclosure, the gas spring 10 includes anoverstroke or overtravel pressure relief feature 18 in the event of anovertravel condition of the piston rod of a gas spring 10 may be used.As will be discussed in greater detail below, the overtravel pressurerelief feature 18 may be part of the guide and seal assembly 14, may bein fluid communication with the pressure chamber 17, and may function toallow pressurized gas to be communicated out of the pressure chamber 17,to provide protection in an overtravel condition, including possibleoverpressure of gas in the pressure chamber 17. The overtravel pressurerelief feature 18 prevents gas in the pressure chamber 17 from exitingthe gas spring 10, absent an overtravel condition associated with thegas spring 10. But in the event of an overtravel condition, theovertravel pressure relief feature 18 may be activated to releasepressurized gas from within the pressure chamber 17 of the gas spring10. As used herein, the terminology “overtravel condition” includes acondition where a die member, or any other machine component with whichthe gas spring 10 interacts, causes the piston rod to be retracted intothe case travels beyond a design intent position in the gas spring 10.

With reference to FIG. 2, the casing 12 may include a side wall 20 thatmay terminate axially at a closed end 22 and at an open end 24 thatreceives the guide and seal assembly 14 and the piston rod 16 therein.The pressure chamber 17 is established at least in part by the side andend walls 20, 22 to receive a gas under pressure. The closed end 22 maybe a separate component attached to the side wall 20, for example by aweld joint, or may be integrally produced with the side wall 20. Theside wall 20 of the casing 12 has an inner surface 26 defining at leastin part the pressure chamber 17, and an outer surface 30. The casing 12may be of generally cylindrical shape, for example, wherein at least oneof the inner or outer surfaces 26, 30 is cylindrical. The inner surface26 of the side wall 20 may have a circumferential retainer groove 32constructed for receipt of a retainer, shown here by way of example as asplit ring 34, to maintain the gas spring 10 in its assembled state. Tofacilitate mounting and locating the gas spring 10 within a press, apair of longitudinally spaced circumferential grooves 36, 38 may bemachined, formed, or otherwise provided in the outer surface 30 of thecasing 12 adjacent its ends 22, 24. To admit gas into the gas spring 10,the casing 12 may include a passage or fill port 40 that may be providedthrough the closed end 22 of the casing 12 in any suitable manner. Thefill port 40 may include a threaded passage 42 for coupling of a fillvalve 41 (such as a Schrader fill valve) to the casing 12. The closedend 22 of the casing 12 also may include a passage 39 in fluidcommunication between and with the pressure chamber 17 and the fill port40.

The guide and seal assembly 14 may be disposed in the open end 24 of thecasing 12 and may be sealingly coupled to the casing 12. The assembly 14may include a piston rod housing 44, a guide bushing 46, a rod seal 48,a seal backup 47, a rod wiper 50, a dust cover 52, an O-ring casing seal54, and a seal backup 56, all of which may be carried by the housing 44.The guide bushing 46 may be composed of any suitable low frictionmaterial, and may be sized to slidably engage the piston rod 16 to guidethe piston rod 16 for axial reciprocation within the casing 12. Thehousing 44 may include a shoulder 45 in an outer surface thereof tocooperate with the split ring 34, which may removably retain the housing44 in the casing 12.

The piston rod 16 is disposed at least in part in the casing 12 andthrough the guide and seal assembly 14 for reciprocation along an axis Abetween extended and retracted positions over a cycle of the gas spring10 including a retraction stroke and an extension or return stroke. Thepiston rod 16 is acted on by pressurized gas in the pressure chamber 17to bias the piston rod 16 toward the extended position, and away fromthe retracted position. The piston rod 16 extends out of the casing 12through the guide and seal assembly housing 44, and includes an outeraxial end, and an inner axial end disposed in the casing 12 and that maybe radially enlarged and engageable with a portion of the piston rodhousing 44 to retain the piston rod 16 in the casing 12. The piston rod16 is in sealing engagement with the rod seal 48 and in slidingengagement with the piston rod bushing 46 for guided relative movementbetween the extended and retracted positions.

The overtravel pressure relief feature 18 may include a hollow rod, pin,or tube 60 carried by the piston rod housing 44 in communication withthe pressure chamber 17 at an interior end 62. The tube 60 extendsaxially proud of or beyond the housing 44 and the casing 12 at anexterior end 64. The interior end 62 may be open, and the exterior end64 may be closed. The tube 60 also extends axially beyond the piston 16when the piston 16 has travelled past a design-intent fully retractedposition, as illustrated in FIGS. 2 and 3, such that an axially outersurface of the piston 16 is located between an axially outer surface ofthe exterior end 64 of the tube 60 and the open end 24 of the casing 12.The tube 60 may be carried in a through passage 66 in the housing 44.The passage 66 may extend axially between and intersects an interior end68 of the housing 44 and an exterior end 70 of the housing 44, andradially between radially inner and outer peripheries of the housing 44.

The tube 60 may be coupled to the housing 44 in any suitable manner. Forexample, the tube interior end 62 may be flared to establish a shoulderto engage the interior end 68 of the housing 44 and axially retain thetube 60 to the housing 44. The tube 60 may have an interference fitwithin the passage 66, for example, by press fit, shrink fit, or in anyother suitable manner. The exterior end 64 of the tube 60 may include ashoulder 72 to engage the exterior end 70 of the housing 44 and axiallyretain the tube 60 to the housing 44. The tube 60 may be axially trappedin the housing 44, for example, where the tube 60 is both flared at theinterior end 68 of the housing 44 and has the shoulder 72 at theexterior end 70 of the housing 44, or in any other suitable manner.

The overtravel pressure relief feature 18 also may include a tubeprotective cover 74 carried around the exterior end 64 of the tube 60.The cover 74 may include a first surface 76 positioned against theexterior end 70 of the housing 44 and a second surface 78 that mayproject axially beyond or flush with an axially outer surface of thetube end 64. The cover 74 may be composed of a deformable foamthermoplastic, or any other suitable deformable or compressablematerial.

The gas spring 10 may be assembled in any suitable manner and itsvarious components may be manufactured in any suitable manner andcomposed of any suitable materials. For example, the casing 12 may beturned, bored, drilled, tapped, and/or otherwise machined from a metaltube and/or metal bar stock such as steel. In another example, the tube60 may be constructed from, for example, steel, brass, copper, carbonfiber, and/or any other suitable material(s). The closed end of the tube60 may be closed by a forming operation, by solder, by adhesive, by aplug, and/or in any other suitable manner. The interior end of the tube60 may be sealed to the housing 44 by a forming operation, by solder, byadhesive, and/or in any other suitable manner. Moreover, a radiallyouter surface of the tube 60 axially spaced from the interior end may besealed to a corresponding radially inner surface of the housing passage66, by a forming operation, by solder, by adhesive, and/or in any othersuitable manner.

In assembly, the guide and seal assembly 14 may be pre-assembled,including the overtravel pressure relief tube 60. As set forth above,the tube 60 may be an interference fit, swaged, adhered, and/or coupledto the housing 44 in any other suitable manner. Thereafter, the pistonrod 16 may be assembled through the housing 44, and the assembly 14 withthe rod 16 therein may be assembled into the casing 12 and retainedtherein in any suitable manner, for example via assembly of the splitring 34.

In operation, and with respect to FIG. 2, any suitable pressurizingdevice (not shown) may be coupled to the port 40 to open the valve 14and introduce pressurized gas into the port 40. Once a desired pressureis reached, the pressurizing device may be retracted to allow the valve41 to close and thereby seal the pressurized gas within the pressurechamber 17.

Thereafter, the gas spring 10 may be used for any suitable purpose and,in the event of an overtravel condition where a machine componenttravels beyond a design intent position with respect to the gas spring10, the machine component strikes the exterior end 64 of the tube 60,resulting in rupture of the tube 60, for instance, at the exterior end64 of the tube 60. Such rupture will allow pressurized gas in thechamber 17 to escape through the ruptured tube 60 to the exterior of thegas spring.

In one embodiment, the tube 60 also could function as an overpressuredevice, for example, wherein the wall thickness of the end portion 64 ofthe tube 60 is suitably calibrated for a correct or desired failurepressure.

FIGS. 4 and 5 illustrate another presently preferred form of an assembly114 (FIG. 4). This form is similar in many respects to the form of FIGS.1-3 and like numerals between the forms generally designate like orcorresponding elements throughout the several views of the drawingfigures. Accordingly, the descriptions of the embodiments areincorporated by reference into one another in their entireties, and adescription of the common subject matter generally may not be repeatedhere.

The assembly 114 may include a piston rod housing 144, and an overtravelpressure relief feature 118 carried by the housing 144. Other portions,like a seal, bearing, and wiper are not shown. The feature 118 mayinclude a hollow rod or tube 160 carried by the piston rod housing 144and may include an interior end 162, and may extend axially proud of orbeyond the housing 144 at an exterior end 164. The tube 160 may becarried in a through passage 166 in the housing 144 that extends axiallybetween and intersects an interior end 168 of the housing 144 and anexterior end 170 of the housing 144.

The tube interior end 162 may be recessed within the interior end 168 ofthe housing 144 and may be flared to establish a shoulder to engage thehousing 144. The tube exterior end 162 may include an enlarged annularbead 172 to engage the exterior end 170 of the housing 144. The tube 160may be axially trapped to the housing 144 between the flared interiorend 168 and the bead 172 at the exterior end 162. The bead 172 may beproduced by axially compressing the tube 160, for example, when the tube160 is manufactured, or after the tube 160 has been assembled to thehousing 144.

With reference to FIG. 5, the exterior end 164 of the tube 160 isconfigured to rupture when struck. For example, in the event of anovertravel condition where a machine component travels beyond a designintent position, the machine component strikes the exterior end 164 ofthe tube 160, resulting in rupture of the tube 160, for instance, at theexterior end 164 of the tube 160. Accordingly, the exterior end 164 maydevelop an aperture 165, which may be a crack, hole, or any othersuitable passage to allow pressurized gas to escape therethrough. In anycase, such rupture will allow pressurized gas in a pressure chamber toescape through the ruptured tube 160.

FIGS. 6-7 illustrate another presently preferred form of an assembly 214(FIG. 6). This form is similar in many respects to the forms of FIGS.1-5 and like numerals between the forms generally designate like orcorresponding elements throughout the several views of the drawingfigures. Accordingly, the descriptions of the embodiments areincorporated by reference into one another in their entireties, and adescription of the common subject matter generally may not be repeatedhere.

The assembly 214 may include a piston rod housing 244, and an overtravelpressure relief feature 218 carried by the housing 244. The feature 218may include a plunger pin 260 carried by the piston rod housing 244 andmay include an interior end 262, and may extend axially proud of orbeyond the housing 244 at an exterior end 264. In the illustratedexample, the pin 260 is hollow and open at both ends but, as discussedherein below, the pin 260 may be solid. The exterior end 264 may beenlarged and configured for press fit retention to the piston rodhousing 244 during an overtravel condition.

For example, the plunger pin 260 may be slidably carried in a blindpassage 266 in the housing 244 that extends axially between ends 268,270 of the housing 244, and intersects the exterior end 270. The pin 260may be installed with an enlarged exterior end 264 in an interferencefit condition with the passage 266. The interference fit may be used tohold the pin in place, especially because since the gas spring may beinverted. The interference fit does not create a large enough force tocounteract the function of piercing the housing when the rod 260 isdriven axially inwardly during an overtravel condition. At the otherend, the passage 266 includes a bottom end or wall 269 at the interiorend 268 of the housing 244, and to which the interior end 262 of the rod260 is proximate or axially adjacent. The bottom wall 269 is relativelythin; thick enough to not rupture under forces due to normal operatingpressures within a gas spring pressure chamber, but thin enough tofacilitate being ruptured by the plunger pin 260 during an overtravelcondition. The pin 260 should be of sufficient wall thickness andmaterial strength so that it is stiff enough to transmit longitudinaldisplacement along its length and not deform itself.

Accordingly, and with reference to FIG. 7, the rod 260 is configured torupture the bottom thin wall 269 during an overtravel condition. Forexample, the interior end 262 of the rod 260 may have one or more spikes263 that may pierce the bottom wall 269 when the rod 260 is drivenaxially inwardly during an overtravel condition. In other embodiments,the interior end 262 of the rod 260 may be pointed or of any othersuitable geometry and may have any other suitable features to pierce orotherwise cut or rupture the bottom wall 269.

In the event of an overtravel condition where a machine componenttravels beyond a design intent position, the machine component strikesthe exterior end 264 of the plunger pin 260, thereby driving the plungerpin 260 into the housing 244 so that the interior end 262 of the rod 262ruptures the thin wall portion 269 of housing 244. Such rupture willallow pressurized gas in a pressure chamber to escape through the hollowor flatted plunger pin 260.

In the embodiment illustrated in FIGS. 6A and 6B, a pin 360 may includea cylindrical or circular body 359 and an axially extending radialrelief 361, such as a groove or a flat. Accordingly, when the pin 360 iscarried in the passage 266 (FIG. 6), a fluid path may be defined betweenthe relief 361 and the passage 266 (FIG. 6). Accordingly, in the eventof an overtravel condition, pressurized gas could flow through theruptured thin wall 269 (FIG. 6), along the relief 361 and out of the gasspring. In other embodiments, the pin 360 may be solid and axiallyrelieved in any other suitable manner, for instance, with one or moreexternal flutes, helical grooves, or any other suitable reliefs.

The overtravel pressure relief feature 218 also may include a protectivecover 174 carried around the exterior end 264 of the rod 260. In thisembodiment, the cover 174 may be a dust cover that may be used toreplace the dust cover 52 of the embodiment of FIGS. 1-3. In otherwords, the protective cover 174 may double as a dust cover. Theprotective cover 174 includes a first surface 176 positioned against theexterior end 270 of the housing 244 and a second surface 178 that isrecessed below an axially outer surface of the exterior end 264 of therod 260. The cover 174 also may include an axially extending annularportion 175 interengaged with the piston rod housing 244 in any suitablemanner, for instance, via interengaging axial shoulders or beads asillustrated.

FIGS. 8 and 9 illustrate another presently preferred form of an assembly314 in which an overtravel pressure relief member may employ a pin thatmay be directly activated by a plate driver. This form is similar inmany respects to the forms of FIGS. 1-7 and like numerals between theforms generally designate like or corresponding elements throughout theseveral views of the drawing figures. Accordingly, the descriptions ofthe embodiments are incorporated by reference into one another in theirentireties, and a description of the common subject matter generally maynot be repeated here.

The assembly 314 may include a piston rod housing 344, and an overtravelpressure relief feature 318 carried by the housing 344. The piston rodhousing 344 may be positioned between the piston rod 316 and theinterior of the casing 312. One or more guide bushings 346 maypositioned between the outer surface of the piston rod 316 and theinside surface of the piston rod housing 344. An O-ring casing seal 354and a support ring 355 may be positioned between the outer surface ofthe piston rod housing 344 and the inner surface of the casing 312, anda rod seal 348 may be positioned between the inside surface of thepiston rod housing 344 and the outer surface of the piston rod 316. Thecasing seal 354 and the rod seal 348 prevent the escape of gas from thepressure chamber 317 to the atmosphere. A retainer groove 332 may beformed on the inner surface of the casing 312, and a split ring 334 maybe positioned in the retainer groove 332 to maintain the piston rodhousing 344 in its assembled state in the housing 344.

A housing fitting or relief pin 360 having a forward or exterior end 361and a rearward or interior end 362 may be carried in an axiallyextending blind bore 366 formed in the piston rod housing 344. Therearward end 362 may have a reduced diameter portion compared to therest of the pin 360. A longitudinal relief 367 (for example, a flat or agroove) may be formed on the outer surface of the pin 360 from theforward end 361 to the rearward end 362 so that a pressure reliefpassage 368 may be formed between the relief 367 and the blind bore 366in the piston rod housing 344 when the pin 360 is positioned in theblind bore 366. An annular channel 370 may be formed in the piston rodhousing 344 that is in fluid communication with the pressure chamber 317and is normally at the same pressure as the gas in the pressure chamber317. A boundary wall 372 may separate the annular channel 370 from therearward end of the axially extending blind bore 366 to prevent theescape of gas from the annular channel 370 through the axial bore 366.The wall 372 may be disposed axially between the annular channel 370 andthe seal 354, and may extend radially outward with respect to the bore366. The interior or rearward end 362 of the pin 360 may be configuredto pierce through the boundary wall 372 in response to an axial forceapplied to the pin 360.

A plate driver 374 may be mounted on the piston rod housing 344 and aplate seal 376 may be positioned in a groove 377 formed in the platedriver 374 and may form a seal between the cylindrical outer surface 378of the plate driver 374 and the interior surface of the casing 312. Arod wiper 379 may be mounted between the outer surface of the piston rod312 and a facing surface 384 of the plate driver 374. The plate driver374 has an outwardly facing drive surface 382 that may be coplanar withthe outward facing drive surface 384 of the piston rod 312, and aninwardly facing bearing surface 386 that may bear on the forward orexterior end 361 of the pin 360.

With reference to FIG. 9, the interior or rearward end 362 of the pin360 is positioned adjacent to the boundary wall 372 formed in the pistonrod housing 344 and is configured to pierce or otherwise breach theboundary wall 372 in response to being driven into the boundary wall.

In the event of an overtravel condition where a machine componenttravels beyond a design intent position, the machine component strikesthe plate driver 374. The plate driver 374 is free to travel rearward asufficient distance to drive the interior or rearward end 362 of the pin360 through the boundary wall 372 into the annular channel 370. Theresulting breach in the boundary wall 372 will allow pressurized gas inthe pressure chamber 317 to escape from the annular channel 370 througha relief path formed by the passageway 368 between the longitudinalrelief 367 on the pin 360 and the bore 366 from the annular channel 370to the outside atmosphere, for example, around the driver 374 or throughany suitable passage or relief therein.

FIGS. 10 and 11 illustrate another presently preferred form of anassembly 414 in which an overtravel pressure relief member may employ abreakable fitting or pin that may be directly activated by a platedriver. This form is similar in many respects to the forms of FIGS. 1-9and like numerals between the forms generally designate like orcorresponding elements throughout the several views of the drawingfigures. Accordingly, the descriptions of the embodiments areincorporated by reference into one another in their entireties, and adescription of the common subject matter generally may not be repeatedhere.

The assembly 414 may include a piston rod housing 444, and an overtravelpressure relief feature 418 carried by the housing 444. The feature 418may comprise the piston rod housing 444 that may be positioned betweenthe piston rod 416 and the interior of the casing 412. The piston rodhousing 444 may have one or more guide bushings 446 that may positionedbetween the outer surface of the piston rod 416 and the inside surfaceof the piston rod housing 444. A casing seal 454 and a seal backup 455may be positioned between the outer surface of the piston rod housing444 and the inner surface of the casing 412, and a rod seal 448 may bepositioned between the inside surface of the piston rod housing 444 andthe outer surface of the piston rod 416. The casing seal 454 and the rodseal 448 prevent the escape of pressurized gas from the pressure chamber417 to atmosphere. A retainer groove 432 may be formed on the innersurface of the casing 412, and a split ring 434 may be positioned in theretainer groove 432 to maintain the piston rod housing 444 in itsassembled state.

An annular channel 470 may be formed in the piston rod housing 444 thatis in fluid communication with the pressure chamber and is normally atthe same pressure as the gas in the pressure chamber. An axial bore 480may extend through the piston rod housing 444 from the annular channel470 to the interior or rearward end of a breakable fitting or pin 460,best seen in FIGS. 11-13. A plate driver 474 may be mounted on thepiston rod housing 444 and may be formed from material such as iron orsteel, or other suitable high strength material. A plate seal 476 may bepositioned in a groove 477 formed in the plate driver 474 and may form aseal between the outer cylindrical surface 478 of the plate driver 474and the interior surface of the casing 412. The plate driver 474 has anoutward facing drive surface 482 that may be parallel with the outwardfacing drive surface 484 of the piston rod 416, and an inward facingbearing surface 486 that may bear on the exterior or forward end or headof the breakable fitting or pin 460. The outward facing drive surface482 of the plate driver may be orthogonal to the axis or normaldirection of travel of the piston rod in the casing.

The breakable fitting or pin 460 is shown in detail in FIGS. 12 and 13.The breakable fitting or pin 460 is not limited to a slender design asshown in connection with FIG. 8, but may be plug shaped and may have ahead and an enlarged diameter body as described herein. The breakablepin 460 may be formed of metal and may have a head 462 and a bodyportion 464 with an axial blind bore 465. The bore 465 extends from alocation just behind a forward or outer axial end wall of the head 462to a rearward or inner axial end of the elongated body 464. In otherwords, the bore 465 may be a blind passage open to an open end of thepin 460 and closed at a closed end of the pin 460.

A portion of the head 462 and the body 464 of the fitting or pin 460 mayincluded a relieved portion 468 to create a weakening 467 in the bodybetween the relieved portion 468 and the bore 465. The relieved portionmay be a chordally extending flat that may be milled into the pin 460,or otherwise machined, formed, or provided therein. The weakening 467could be a single feature or multiple features to allow rupture or shearbut not detachment. The fitting or pin 460 also may include a threadedportion 461 for threaded coupling to a corresponding threaded portion ofthe bore 465. Also, the pin 460 may carry a seal 463 between thethreaded portion 461 and the head 462 to seal the pin to the bore 465.

In the event of an overtravel condition where a machine componenttravels beyond a design intent position, the machine component strikesthe plate driver 474. The plate driver 474 is free to travel rearward asufficient distance to impact the head 462 of the breakable pin 460,rupturing the weakening 467 in the body. The rupture will allowpressurized gas in a pressure chamber to escape from the annular channel470 and through the axial bore in the piston rod housing 444, throughthe bore 465 in the breakable pin 460, and through the rupture thatoccurs in the breakable pin to the atmosphere.

FIGS. 14-16 illustrate another presently preferred form of an assembly514 in which an overtravel pressure relief member may employ a breakablehousing fitting that may be directly activated by a die. This form issimilar in many respects to the forms of FIGS. 1-13 and like numeralsbetween the forms generally designate like or corresponding elementsthroughout the several views of the drawing figures. Accordingly, thedescriptions of the embodiments are incorporated by reference into oneanother in their entireties, and a description of the common subjectmatter generally may not be repeated here.

Referring to FIGS. 14 and 15, the assembly 514 may include a piston rodhousing 544, and an overtravel pressure relief feature 518 carried bythe housing 544. The feature 518 may be positioned between the pistonrod 516 and the interior of the casing 512. The piston rod housing 544may comprise one or more guide bushings 546 that may be positionedbetween the outer surface of the piston rod 516 and the inside surfaceof the piston rod housing 544. A casing seal 554 may be positionedbetween the outer surface of the piston rod housing 544 and the innersurface of the casing 512, and a rod seal 548 may be positioned betweenthe inside surface of the piston rod housing 544 and the outer surfaceof the piston rod 516. The casing seal 554 and the rod seal 548 preventthe escape of pressurized gas from a pressure chamber 517 to theatmosphere.

An annular channel 570 may be formed in the piston rod housing 544 thatis in fluid communication with the pressure chamber 517 and is normallyat the same pressure as the gas in the pressure chamber 517. An axialpassage 580 may extend through the piston rod housing 544 from theannular channel 570 to the rearward end of a breakable pin or housingfitting 560. A retainer groove 532 may be formed on the inner surface ofthe casing 512, and a split ring 534 may be positioned in the retainergroove 532 to maintain the piston rod housing 544 in its assembledstate. A plastic protector 590 may be inserted into the open end of thecasing 512 and surrounds the forward end of the piston rod housing 544.The plastic protector 590 may extend beyond the end of the open end ofthe casing 512 and may contain a mounting aperture 592 that receives abreakable housing fitting 560.

The breakable housing fitting 560 is shown in detail in FIG. 16. Thebreakable housing fitting 560 may have a head 562 and an elongated body564 that may be formed with an axial blind bore 565. The bore 565extends from a location just behind a forward or outer axial end wall ofthe head 562 to a rearward or inner axial end of the elongated body 564.In other words, the bore 565 may be a blind passage open to an open endof the pin 560 and closed at a closed end of the pin 560. The bore 565may extend from just behind the head 562 to the rearward end 566 of theelongated body 564.

The head 562 may have a relieved portion 568 which reduces the thicknessof the material of the body 564 between the relieved portion 568 and thebore 565, and as a result creates a weakening 567 in the body 564 in theregion of the relieved portion 568. The bore 565 communicates with theaxial passage 580 through the piston rod housing 544 that communicateswith the annular channel 570 formed in the piston rod housing 544. Therelieved portion may be a chordally extending flat that may be milledinto the pin 560, or otherwise machined, formed, or provided therein.The pin 560 also may include a threaded portion 561 for threadedcoupling to a corresponding threaded portion of the bore 565. Also, thepin 560 may carry a seal 563 between the threaded portion 561 and thehead 562 to seal the pin 560 to the bore 565.

In the event of an overtravel condition where a machine componenttravels beyond a design intent position, the machine component strikesthe end of the plastic protector 590. The plastic protector 590 willdeform under the force of the machine component, and continued travel ofthe machine component will impact the head 562 of the breakable housingfitting 560, fracturing or rupturing the weakening 567 in the fitting560. The rupture will allow pressurized gas in a pressure chamber toescape from the annular channel 570, through the axial passage 580 inthe piston rod housing 544, through the bore 565 in the breakablehousing fitting 560, and through the break that occurs in the weakening567 in the rupturable housing fitting 560 to the atmosphere.

FIG. 17 illustrates another presently preferred form of an assembly 614in which an overtravel pressure relief member may employ a pin that maybe directly activated by a die. This form is similar in many respects tothe forms of FIGS. 1-16 and like numerals between the forms generallydesignate like or corresponding elements throughout the several views ofthe drawing figures. Accordingly, the descriptions of the embodimentsare incorporated by reference into one another in their entireties, anda description of the common subject matter generally may not be repeatedhere.

The assembly 614 may include a piston rod housing 644, and an overtravelpressure relief feature 618 carried by the housing 644. The feature 618may comprise a piston rod housing 644 that may be positioned between theouter cylindrical surface of the piston rod 616 and the interior of thecasing 612. The piston rod housing 644 may comprise a body that may haveone or more guide bushings 646 that may positioned between the outersurface of the piston rod 616 and the inside surface of the piston rodhousing 644. A casing seal 654 may be positioned between the outersurface of the piston rod housing 644 and the inner surface of thecasing 612, and a rod seal 648 may be positioned between the insidesurface of the piston rod housing 644 and the outer surface of thepiston rod 616. The casing seal 654 and the rod seal 648 prevent theescape of pressurized gas from the pressure chamber 617 to atmosphere.

An annular channel 670 may be formed in the piston rod housing 644 thatis in fluid communication with the pressure chamber 617. A boundary wall672 may separate the annular channel 670 from an axially extending blindbore 666 formed in the piston rod housing 644. A retainer groove 632 maybe formed on the inner surface of the casing 612, and a split ring 634may be positioned in the retainer groove 632 to maintain the piston rodhousing 644 in its assembled state. The boundary wall 672 may bedisposed axially between the annular channel 670 and the seal 654, andmay extend radially outward with respect to the blind bore 666.

A plastic protector 690 may be inserted into the open end of the casing616 and surrounds the forward end of the piston rod housing 644. Theplastic protector 690 may extend beyond the end of the open end of thecasing 616 and may contain an axial bore 680 that receives an elongatedpin 660.

The elongated pin 660 may be similar to the pin 360 shown in FIGS. 8 and9. The elongated pin 660 has a forward end 661 and a rearward end 662and a longitudinal relief, for example a flat 667, may be formed on theouter surface of the pin 660 so that a pressure relief passage may beformed between the 667 flat and the axial bore 666 in the piston rodhousing 644 when the pin 660 is positioned in the axial bore 666. Therearward end 662 of the elongated pin 660 may be configured to piercethrough or otherwise rupture the boundary wall 672 in response to anaxial force applied to the pin 660.

In the event of an overtravel condition where a machine componenttravels beyond a design intent position, the machine component strikesthe end of the plastic protector 690. The plastic protector 690 willdeform under the force of the machine component, and continued travel ofthe machine component will impact the forward end of the pin 660 andwill drive the rearward end 662 of the pin 660 through the boundary wall672 into the annular channel 670. The breach in the boundary wall 672will allow pressurized gas in the pressure chamber to escape from theannular channel 670 through the passageway formed between thelongitudinal flat 667 on the pin 660 and the bore 666 through the pistonrod housing 644 to atmosphere.

The embodiments of FIGS. 8, 9, and 17 include an overtravel pressurerelief pin 360, 660 carried in a blind bore 366, 666 of a piston rodhousing 344, 644 and having an exterior end 361, 661 for contact with adriving member and an interior end 362, 662 for rupturing a portion ofthe piston rod housing 344, 644 when the driving member drives the pin360, 660 further into the piston rod housing 344, 644, and wherein thepin 360, 660 may have a longitudinally extending relief 367, 667 todefine an overpressure relief passage between the pin 360, 660 and thepiston rod housing 344, 644.

The embodiments of FIGS. 10-16 include an overtravel pressure reliefmember pin 460, 560 carried in a through bore 480, 580 of the piston rodhousing 444, 544 and having an open end, a blind bore 465, 565 in theopen end and terminating at a closed exterior end 462, 562 for contactwith a driving member, wherein the exterior end 462, 562 has a weakening467, 567 to rupture the pin 460, 560 when the driving member drives thepin 460, 560 toward the piston rod housing 444, 544, and wherein the pin460, 560 also may have a threaded portion 461, 561 threaded into acorresponding threaded portion of the through bore 480, 580 of thepiston rod housing 444, 544 and the weakening 467, 567 may be achordally extending flat in a side of the closed exterior end 462, 562of the pin 460, 560.

In any of the embodiments disclosed herein, the driving member may be amachine component, for example, a die plate, or the driving member maybe a plate or the like coupled to the piston rod.

In one or more of the forms disclosed herein, the overtravel pressurerelief member does not fail during normal use from gas pressurefluctuations in the pressure chamber, for example, over 150-300 bar.Also, the member is retained during an overtravel condition to preventany secondary hazard. The overtravel pressure relief feature isconfigured to discharge pressure with overtravel on the order of 0.5 to1.5 mm. The overtravel pressure relief feature allows for normaloperation of a gas spring and is configured for retrofit of existingproducts, which also can be serviced by an existing product repair kitand procedure.

FIGS. 18-22 illustrate another presently preferred form of an assembly714. This form is similar in many respects to the forms of FIGS. 1-17and like numerals between the forms generally designate like orcorresponding elements throughout the several views of the drawingfigures. Accordingly, the descriptions of the embodiments areincorporated by reference into one another in their entireties, and adescription of the common subject matter generally may not be repeatedhere.

With reference to FIGS. 18-20, the assembly 714 includes a piston rodhousing 744, and an overtravel pressure relief pin 760 carried by thehousing 744. With reference to FIG. 20, the assembly 714 also mayinclude one or more guide bushings 746, a rod wiper 750, an O-ringcasing seal 754, a support ring 755, and a rod seal 748. The relief pin760 has a forward or exterior end 761 and a rearward or interior end762, and is carried in a blind passage 766 of the piston rod housing 744extending between interior and exterior ends of the housing 744.

With reference to FIG. 21, at the interior end of the housing 744, asidewall includes a longitudinally extending portion 771 and may includea seal groove flange 773 extending radially outwardly therefrom belowthe seal 754. The sidewall also includes a wall dimple 772 that may bedisposed between the seal groove flange 773 and the interior end of thehousing 744 and, in any case, intersects the passage 766, for example,by projecting into the passage 766. The wall dimple 772 may besemi-spherical as illustrated or may be rectangular, or of any othersuitable shape. In any case, the wall dimple 772 may be produced in athinned wall portion 777 of the sidewall of the housing 744. The thinnedwall portion 777 may be produced by turning an outer diameter of thesidewall, for example, in a location below or behind the flange 773 toachieve a desired reduced wall thickness. Then, the dimple 772 may beproduced by indenting or otherwise deforming or displacing the thinnedwall portion 777 with a punch, or any other suitable tool.

With reference to FIGS. 22-23, the pin 760 includes a shearing portion793 at the interior end 762, and a venting portion 767 extending fromthe shearing portion 793 toward the exterior end 761. The shearingportion 793 of the pin 760 may include a cylindrical head or a head ofany other suitable shape. The shearing portion 793 may be interferencefit in the passage 766 (FIG. 21) and may be used to rupture the dimple722 during an overtravel condition, as well as an aid in retaining thepin 760 to the housing 744 (FIG. 21) after the overtravel condition. Theventing portion 767 may include a semi-cylindrical head 794 having aflat 795 at the exterior end 761 and an intermediate portion 796 havinga radial size less than that of at least one of the cylindrical head orthe semi-cylindrical head 794. The head 794 may be interference fit in acorresponding portion of the passage 766 (FIG. 20). The intermediateportion 796 may be cylindrical or of any other suitable shape.Accordingly, with reference to FIGS. 20 and 23, a pressure reliefpassage may be formed between the venting portion 767 (FIG. 23) and theblind passage 766 (FIG. 20) in the piston rod housing 744 (FIG. 20) whenthe pin 760 is positioned in the blind passage 766 (FIG. 20).

With reference to FIG. 21, the interior or rearward end 762 of the pin760 is positioned adjacent to the dimple 772 in the piston rod housing744 and is positioned to pierce or otherwise breach the dimple 772 inresponse to being driven into the dimple 772 as a result of an axialforce applied to the pin 760. For example, in the event of an overtravelcondition where a machine component travels beyond a design intentposition, the pin 760 is driven into the housing 744 such that theinterior or rearward end 762 of the pin 760 is driven into the walldimple 772 and through at least a portion thereof to shear at least aportion of the dimple 772. The resulting breach in the dimple 772 allowspressurized gas to escape through a relief path including the passage766 and opened by the ruptured dimple 772 and extending between the pin760 and the housing 744 through the passage 766 to the outsideatmosphere.

Still referring to FIG. 21, a distance between the interior end of thepin 760 in an as-assembled state of the assembly 714, and the interiorend of the pin 760 in an as-ruptured state of the assembly 714, may be,for example, 0.5 to 1.0 mm. Those of ordinary skill in the art willrecognize that any suitable such dimension may be chosen for any givenspecific application. In any case, after rupture, the pin 760 isretained in the housing 744 via the interference fit of the vented headof the pin 760 and the housing 744 and/or via the sealing head of thepin 760 and the housing 744.

FIGS. 24-25 illustrate another presently preferred form of an assembly814. This form is similar in many respects to the forms of FIGS. 1-23and like numerals between the forms generally designate like orcorresponding elements throughout the several views of the drawingfigures. Accordingly, the descriptions of the embodiments areincorporated by reference into one another in their entireties, and adescription of the common subject matter generally may not be repeatedhere.

The assembly includes a housing 844 having a blind passage 866 carryingthe pin 760, and is substantially similar to the assembly 714 of FIGS.18-23. But, as illustrated in FIG. 25, a thinned wall portion 877 may beestablished by milling a portion of a sidewall of the housing 844instead of by a turning operation. For example, the thinned wall portion877 may include a bottom wall of a milled pocket 897 as illustrated, ormay include a simple spot face, or any other suitable machining,coining, or forming feature. A wall dimple 872 may be established by anysuitable tool after a milling operation, or by a blunt end of a millingtool, or in any other suitable manner. The wall dimple 872 intersectsthe passage 866 for cooperation with the pin 760 as previouslydescribed.

One or both of the embodiments of FIGS. 18-25 may enable an easierhousing rupture configuration with a shorter pin stroke, which maytranslate into less actuation-to-venting and less force required toachieve venting. Also, dimpling the housing wall may work harden thehousing material, and use of the wall dimple may provide a housing wallwith good structural integrity and reduced risk of leakage.

FIGS. 26-27 illustrate another presently preferred form of a piston rodhousing 944. This form is similar in many respects to the form of FIGS.1-25 and like numerals between the forms generally designate like orcorresponding elements throughout the several views of the drawingfigures. Accordingly, the descriptions of the embodiments areincorporated by reference into one another in their entireties, and adescription of the common subject matter generally may not be repeatedhere.

The piston rod housing 944 has an integral overtravel pressure relieffeature 918, which may include a passage 966 extending through thehousing 944, and a hollow projection 960 in fluid communication with thepassage 966. The hollow projection 960 establishes a portion of thepassage 966, projects from the exterior end 970 of the housing 944, andterminates in a closed end 964. The hollow projection 960 is an integralportion of the piston rod housing 944. The passage 966 generally extendsbetween an interior end 968 of the housing 944 and an exterior end 970of the housing 944. The feature 918 also includes an interior end 962 aswell as the closed exterior end 964 of the projection 960. Asillustrated, the interior end 962 need not intersect the interior end968 of the housing 944, although it may in other embodiments. In thisembodiment, however, the passage 966 includes a predominantlylongitudinally extending branch, and a radially or transverselyextending branch at the interior end 962 that opens in a location belowor behind a seal groove as shown.

As illustrated, the passage 966 need not be straight and, instead, mayfollow a tortuous path. Accordingly, the feature 918 and the rest of thehousing 944 may be produced by stereolithography, or a three-dimensionalprinting operation that produces the housing 944 and that may includelaser sintering, or in any other suitable manner. In embodiments wherethe passage 966 is straight, the feature and the rest of the housing maybe produced by a machining operation that produces the housing.

The hollow projection 960 projects beyond the exterior end 970 of thehousing 944. Accordingly, the exterior end 964 of the feature 918 isconfigured to rupture when struck. For example, in the event of anovertravel condition where a machine component travels beyond a designintent position, the machine component strikes the exterior end 964 ofthe projection 960, resulting in rupture of the projection 960, forinstance, at the exterior end 964 thereof. Accordingly, the exterior end964 may develop an aperture, which may be a crack, hole, or any othersuitable passage to allow pressurized gas to escape therethrough. In anycase, such rupture will allow pressurized gas in a pressure chamber toescape through the ruptured projection 960. The projection 960 may beconfigured similarly as the fittings 460, 560 previously described.

It should be appreciated that one of ordinary skill in the art willrecognize other embodiments encompassed within the scope of thisinvention. The plurality of arrangements shown and described above aremerely illustrative and not a complete or exhaustive list orrepresentation. Of course, still other embodiments and implementationscan be achieved in view of this disclosure. The embodiments describedabove are intended to be illustrative and not limiting. The scope of theinvention is defined by the claims that follow.

The invention claimed is:
 1. A piston rod housing assembly for a gasspring, comprising: a piston rod housing including: an annular sidewallconfigured to slidably receive a piston rod; an interior end, anexterior end axially spaced from the interior end, an overtravelpressure relief passage extending generally axially in the sidewall ofthe piston rod housing and intersecting the exterior end; and anovertravel pressure relief member carried in the overtravel pressurerelief passage having an exterior end and projecting axially beyond theexterior end of the piston rod housing; and a protective cover carriedaround the exterior end of the overtravel pressure relief member.
 2. Theassembly of claim 1, wherein the overtravel pressure relief membercomprises a hollow projection establishing a portion of the overtravelrelief passage, projecting from the exterior end, and terminating in aclosed end.
 3. The assembly of claim 2, wherein the projection is anintegral portion of the piston rod housing.
 4. The assembly of claim 1,further comprising: the overtravel pressure relief member carried in theovertravel pressure relief passage and having an exterior end thatprojects axially beyond the piston rod housing.
 5. The assembly of claim4, wherein the overtravel pressure relief member is a pin having alongitudinally extending relief to define an overpressure relief passagebetween the pin and the piston rod housing.
 6. The assembly of claim 4,wherein the overtravel pressure relief member is a tubular memberwherein the exterior end is closed.
 7. The assembly of claim 6, whereinthe tubular member includes an interior end that is open.
 8. Theassembly of claim 6, wherein the tubular member is coupled to thehousing by at least one of an interference fit, swaging, adhesive, orsolder.
 9. The assembly of claim 6, wherein the tubular member iscomposed of at least one of steel, copper, brass, or carbon fiber. 10.The assembly of claim 4, wherein the overtravel pressure relief passageis a through passage that also intersects the interior end of the pistonrod housing, and the overtravel pressure relief member is a tubularmember wherein the exterior end thereof is closed.
 11. The gas spring ofclaim 4, wherein the overtravel pressure relief member is a pin carriedin a blind passage of the piston rod housing and having an exterior endfor contact with a driving member and an interior end to rupture aportion of the piston rod housing when the driving member drives the pinfurther into the piston rod housing.
 12. The assembly of claim 11,wherein the overtravel pressure relief member includes a hollow rod or asolid pin with an axially extending radial relief, having an interiorend with at least one spike and wherein the exterior end is enlarged andconfigured for press fit retention to the piston rod housing during anovertravel condition.
 13. The assembly of claim 11, wherein the pinincludes a shearing portion at the interior end, and a venting portionextending from the shearing portion toward the exterior end.
 14. Theassembly of claim 13, wherein the shearing portion of the pin includes acylindrical head, and the venting portion includes a semi-cylindricalhead having a flat at the exterior end and an intermediate portionhaving a radial size less than that of at least one of the cylindricalhead or the semi-cylindrical head.
 15. The assembly of claim 4, whereinthe overtravel pressure relief member is a pin carried in a blindpassage of the piston rod housing and having an exterior end for contactwith a driving member and an interior end for rupturing at least one ofa bottom wall or a dimpled sidewall of the piston rod housing when thedriving member drives the pin further into the piston rod housing.
 16. Apiston rod housing assembly for a gas spring, comprising: a piston rodhousing including: an annular sidewall configured to slidably receive apiston rod; an interior end, an exterior end axially spaced from theinterior end, an overtravel pressure relief blind passage extendinggenerally axially in the sidewall of the piston rod housing andintersecting the exterior end; a wall dimple intersecting the blindpassage and configured to be ruptured by the pin during an overtravelcondition; and an overtravel pressure relief pin carried in theovertravel pressure relief blind passage and having an exterior endprojecting axially beyond the exterior end of the piston rod housing forcontact with a driving member and an interior end to rupture the dimplewhen the driving member drives the pin further into the piston rodhousing.
 17. The assembly of claim 16 wherein the housing also has awall thinning, wherein the dimple is in the wall thinning.
 18. A pistonrod housing assembly for a gas spring, comprising: a piston rod housingincluding: an annular sidewall configured to slidably receive a pistonrod; an interior end, an exterior end axially spaced from the interiorend, an overtravel pressure relief blind passage extending generallyaxially in the sidewall of the piston rod housing and intersecting theexterior end; and an overtravel pressure relief pin carried in the blindpassage in the piston rod housing, projecting axially beyond theexterior end of the piston rod housing, and having an open end, a blindpassage in the open end and terminating at a closed exterior end forcontact with a driving member, wherein the exterior end has a weakeningto rupture the pin when the driving member drives the pin toward thepiston rod housing.
 19. The assembly of claim 18, wherein the pin alsohas a threaded portion threaded into a corresponding threaded portion ofthe through bore of the piston rod housing and the weakening is achordally extending flat in a side of the closed exterior end of thepin.
 20. A gas spring for forming equipment, comprising: a casingincluding an axially extending side wall, an open end, a transverselyextending closed end wall axially spaced from the open end, a pressurechamber established in part by the side and end walls to receive a gasunder pressure; a piston rod received at least in part in the casing forreciprocation between extended and retracted positions; a piston rodhousing having an annular sidewall received at least in part in the openend of the casing, slidably receiving the piston rod, an interior endcommunicating with the pressure chamber, and an exterior end axiallyspaced from the interior end and adjacent the open end of the casing; anovertravel pressure relief passage extending generally axially in theannular sidewall and intersecting the exterior end of the annularsidewall; an overtravel pressure relief member carried in the overtravelpressure relief passage and having an exterior end that projects axiallybeyond the exterior end of the piston rod housing and the open end ofthe casing; and a protective cover carried around the exterior end ofthe overtravel pressure relief member and including a first surfacepositioned against the exterior end of the housing and a second surfacethat is flush with or projects axially beyond an axially outer surfaceof the exterior end of the overtravel pressure relief member.
 21. Thegas spring of claim 20, further comprising: the overtravel pressurerelief member carried in the overtravel pressure relief passage andhaving an exterior end that projects axially beyond the piston rodhousing; and the protective cover having a surface that is recessedbeneath an axially outer surface of the exterior end of the overtravelpressure relief member, and also includes an axially extending annularportion interengaged with the piston rod housing.
 22. A gas spring forforming equipment, comprising: a casing including an axially extendingsidewall, an open end, a transversely extending closed end wall axiallyspaced from the open end, and a pressure chamber defined in part by theside and end walls to receive a gas under pressure; a piston rodreceived at least partially in the casing for reciprocation betweenextended and retracted positions; a piston rod housing having an annularsidewall received at least in part in the open end of the casing,slidably receiving the piston rod, an interior end communicating withthe pressure chamber, and an exterior end axially spaced from theinterior end and adjacent the open end of the casing; an overtravelpressure relief blind passage extending generally axially in the annularsidewall and intersecting the exterior end of the annular sidewall; anda pin carried in the blind passage of the piston rod housing, projectingaxially beyond the exterior end of the piston rod housing and the openend of the casing for contact with a driving member, and an interior endfor rupturing at least one of a portion of the interior end of thepiston rod housing or a dimpled sidewall portion of the piston rodhousing projecting into the blind passage when the driving member drivesthe pin further into the piston rod housing to enable gas under pressurein the pressure chamber to escape through the blind passage to theexterior of the gas spring via the ruptured portion of the interior endof the piston rod housing and/or ruptured dimpled sidewall portion ofthe piston rod housing.